Finishing method

ABSTRACT

Workpieces are finished in a vibratory or tumbling finishing apparatus by means of chips containing abrasive grains in an ice matrix. During finishing, a hydrocarbon-based liquid refrigerant chilled below the melting temperature of the ice matrix is circulated through a vibrating admixture of workpieces and chips.

United States Patent 1191 1111 3,745,722 Balz 1451 July 17, 1973 FINISHING METHOD 3,676,963 7 1972 Rice 5l/l64.5 x

[75] Inventor: Gunther W. Balz, Kalamazoo, Mich.

[73] Assignee: Roto-Finish Company, Kalamazoo, Primary Examiner D0nald Kelly Mi h Attorney-Gordon W. l-lueschen et al.

[22] Filed: Sept. 13, 1971 21 A l. N 1 8 1 p 0 80,08 57 ABSTRACT US. Cl. workpieces are finished in a ibratory or tumbling fin- [5 apparatus means of chips containing abrasive Fleld of Search 164.5, grains in an ice n' atrix During finishing a hydrocar. 164 bon-based liquid refrigerant chilled below the melting temperature of the ice matrix is circulated through a References Cited vibrating admixture of workpieces and chips.

UNITED STATES PATENTS 6/1967 Lester 51/314 14 Claims, N0 Drawings BACKGROUND OF THE INVENTION This invention relates to finishing of hard-surface articles such as metal, plastic, and ceramic parts, or the like. Typical of such workpieces are castings, forgings, stampings, and the like. The term finishing as used herein is used in a broad sense and is taken to mean any and all of the usual surface treatments such as polishing, grinding, descaling, bumishing, cleaning, or similar operations when implemented by vibration or tumbling.

Finishing operations on the aforementioned workpieces can be conveniently carried out with excellent results in vibratory-type finishing machines such as those exemplified by U.S. Pat. No. Re. 27,084, as well as machines disclosed and claimed in U.S. Pat. No. 3,071,900; U.S. Pat. No. 3,073,069; U.S. Pat. No. 3,073,078; U.S. Pat. No. 3,073,079; U.S. Pat. No. 3,073,080; U.S. Pat. No. 3,073,081; U.S. Pat. No. 3,073,082; and U.S. Pat. No. 3,093,940.

Such finishing methods generally involve the admixing of workpieces with solid abrasive media commonly referred to as chips" and thereafter subjecting the admixture of workpieces and chips to macroorbital motion by vibration or tumbling. The chips can be pebbles of natural stone, chunks of crushed rock, or shaped abrasive materials such as grains of aluminum oxide, silicon carbide,-diamond, sand, and the like, held together in a binding matrix. While various materials can be utilized as binders for the manufacture of shaped chips, one such material enjoying increasing acceptance and use in the finishing arts is ice. Chips containing abrasive grains in an ice matrix are disclosed in U.S. Pat. No. 3,324,605.

However, inasmuch as, during finishing, heat is generated within the working mass and most of the finishing is normally done in work areas maintained at ambient temperatures, the useful life of an ice-based finishing chip is relatively short, usually being of the order of about 30 minutes. Attempts to prolong the useful life have been made and are disclosed in said U.S. Pat. No. 3,324,605. It has been tried to supercool the ice-based chips prior to introduction into the finishing machine. Also, cooling jackets around the workpiece-containing chamber of a finishing machine have been provided. Nevertheless, all of these heretofore attempted methods are cumbersome and have not met with unequivocal success and/or acceptance.

Accordingly, it is an object of the present invention to provide a method for finishing workpieces using icebased chips whereby the useful life'of the chips is substantially prolonged without the attendant aforementioned shortcomings. Still other objects will present I themselves to one skilled in the art upon reference to the ensuing specification and the claims.

SUMMARY OF THE INVENTION The present invention contemplates providing finishing chips containing abrasive drains in an ice matrix, admixing workpieces to be finished with the finishing chips, imparting macroorbital motion to the resulting admixture, and circulating through the admixture a hydrocarbon-based liquid refrigerant chilled to a temperature below the melting temperature of the ice matrix.

In one preferred embodiment of this invention, the finishing chips are manufactured by casting a slurry of mud-like consistency into a mold having a desired shape and which is submerged in a chilled liquid refrigerant bath. The same liquid refrigerant is then circulated from the bath through the admixture of workpieces and chips in the finishing machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Chips that are employed in the finishing process can be of any desired shape depending on the finishing requirements for the particular workpieces. Suitable contours are those of a bar, nugget, cylinder, cone, cube, multi-faceted prism, tube, ring, star, and the like. Compared to the size of the abrasive grains in the chip, the chip is relatively large. Common chip sizes range from nuggets about one centimeter in diameter to prisms measuring about 5 centimeters on an edge. The abrasive grains can be dispersed uniformly through the ice matrix of the finishing chip, or the grains can be concentrated at surface, center, or a particular region of the chip, as desired.

The finishing chips can be conveniently manufactured by admixing abrasive grains such as sand, aluminum oxide, silicon carbide, diamond, quartz, boron carbide, zircon, and the like, with water so as to form a slurry of mud-like consistency, casting the slurry into a mold having cavities of predetermined shape depending on the desired contour for the chip, and solidifying the cast slurry in the mold cavities by chilling to a temperature below the solidification temperature of the slurry. Upon solidification, the chips are ready for immediate use in a vibratory or tumbling finishing machine, or the chips can be stored under refrigeration for subsequent use. Chilling of the slurry can be conveniently accomplished by immersing the mold into a bath of the hydrocarbon-based liquid refrigerant suitably cooled to a sufficiently low temperature. Also, the solidified chips can be dislodged from the mold while still submerged in the liquid refrigerant bath and stored there until used.

While surface finishing using chips containing abrasive grains suspended in an ice matrix can be carried out at any temperature, the chips themselves, of course, should be maintained at or below the melting temperature of the ice matrix. It has been found that the maximum hardness of the ice matrix is obtained at about 20F. (-29C.), thus in many finishing processes it is preferred to maintain the chips at this temperature during finishing. Temperatures below about 40F. (40C.) do not contribute to the finishing process, but may tend to embrittle the workpieces or parts of the apparatus, and for such reasons are undesirable.

Temperature control of the chips, and of the macroorbiting mass comprising workpieces and chips in the finishing machine, is achieved according to the present invention by circulating through the mass a suitably chilled hydrocarbon-based liquid refrigerant. It is essential that the refrigerant be circulated. Sludge buildup within the finishing chamber and caking of the individual chips is thereby minimized or prevented. Where the chips have been chilled during manufacture by immersion into a hydrocarbon-based liquid refrigerant bath, it is convenient to utilize the same refrigerant also during finishing by circulating the chilled hydrocarbon-based liquid from the bath through the admixture of chips and workpieces.

During finishing, either in a vibrating chamber or by tumbling, the admixture of chips and workpieces macroorbits or rolls within the finishing chamber. Thus it is not necessary to completely fill the chamber containing the admixture with the chilled liquid refrigerant during processing of the workpieces. As a matter of fact, in many instances such a condition may be undesirable, particularly in a vibratory finishing machine, because of possible interference of the liquid with the vibratory action working on the chip and workpiece admixture and causing it to macroorbit as well as causing the chips and the workpieces to travel in individual microorbital paths at the same time. It is sufficient that the circulating chilled liquid refrigerant is present only in the lower portion of the finishing chamber because during finishing all of the chips will eventually come in contact with the refrigerant due to the aforedescribed macroorbital motion.

The hydrocarbon-based liquid refrigerant can be present in the vibrating bowl in an amount up to about l5 percent by volume of the vibrating admixture and preferably in an amount of about 5 to about percent by volume of the vibrating admixture.

In addition to chilling the finishing chips, the liquid refrigerant also exerts an influence on the type of finish that can be produced on the workpieces and thus additionally functions as a finishing compound. For example, a more viscous refrigerant liquid will produce a finer finish; however, the cutting rate will be somewhat reduced. In addition, the solvent action of the liquid refrigerant aids in removing oils, cutting fluids, and similar substances that may be present on the workpieces as well as performs the function of carrying away fines generated by the abrasive action of the chips during the finishing process. The degreasing and/or detergent properties of the liquid refrigerant, in general, will exert an influence on the type of finish that can be obtained.

Hydrocarbon-based liquid refrigerants suitable for practicing the present invention are those which are liquids below the freezing point of water and within the temperature range of the finishing process. Such liquid refrigerants can be liquid hydrocarbons such as naphtha, kerosene, mineral spirits (Stoddard Solvent), and the like, and halogenated liquid hydrocarbons such as l,l,l-trichloroethane, methyl chloride, methylene chloride, carbon tetrachloride, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, monochlorodifluoromethane, trichlorotrifluoroethane, dichlorotetrafiuoroethane, and the like. Of the liquid hydrocarbon refrigerants particularly preferred are naphtha and mineral spirits i.e., Stoddard Solvent. Of the halogenated liquid hydrocarbons particularly preferred is l, l l -trichloro-ethane.

The liquid refrigerant can be chilled in any convenient manner such as by cooling coils or similar heat exchange means. The refrigerant can be introduced into the finishing chamber such as a vibrating bowl through a spray header or similar liquid distributing means situated above the bowl and drained therefrom through a suitable drain means or near the bottom of the vibrating bowl. Suitable apparatus arrangement for circulation of the refrigerant liquid is shown in US Pat. No. 3,161,997.

The present invention is further illustrated by the following examples.

EXAMPLE l Sand castings of aluminum are admixed in the finishing chamber of a tub-type vibratory finishing machine with finishing chips containing finely divided silicone dioxide particles suspended in an ice matrix. A macroorbital motion is then imparted to the admixture for about 45 minutes by suitably vibrating the finishing chamber.

When the finishing process is carried out without recirculation of a chilled liquid refrigerant through the vibrating admixture, surface finish on the castings is relatively dark and the macroorbital motion cannot be sustained toward the end of the run because of sludge formation in the chamber, melting ice, and caking of the finishing chips.

On the other hand, when a chilled liquid refrigerant is circulated through the admixture during the finishing process, a brighter, cleaner finish is imparted to the castings, and the chips remaining in the finishing chamber are ready for further use.

EXAMPLE ll The finishing chamber of a toroidal bowl-type vibratory finishing machine is filled with finishing chips con taining finely-divided silicon dioxide particles suspended in an ice matrix. The finishing chips are then permitted to stand at ambient temperature. After about 4 to 6 hours the chips have melted and a mud cake is formed in the finishing chamber which is difficult to clean out and which clogs up the finishing chamber drain.

EXAMPLE Ill The finishing chamber of a toroidal bowl-type vibratory finishing machine is filled with finishing chips of the same type and configuration as in Example ll, above. Mineral spirits (Stoddard Solvent) maintained at about 20F. (29C.) is then circulated through the chips in the finishing chamber. At the end of a twoweek period no bonding or caking of the chips is observed and the chips are ready for immediate use.

The foregoing discussion and the examples are intended as illustrative but are not to be construed as limiting. Still other variations and embodiments within the spirit and scope of this invention are possible and will readily present themselves to one skilled in the art.

I claim:

1. A method of finishing workpieces in a finishing machine which comprises admixing said workpieces with chips containing abrasive grains in an ice matrix, imparting macroorbital motion to the resulting admixture, and circulating through the admixture a liquid refrigerant comprising a material selected from the group consisting of hydrocarbons and halogenated hydrocarbons chilled to a temperature below the melting temperature of the ice matrix.

2. The method in accordance with claim 1 wherein the liquid refrigerant is mineral spirits.

3. The method in accordance with claim 1 wherein the liquid refrigerant is naphtha.

4. The method in accordance with claim 1 wherein the liquid refrigerant is a halogentated hydrocarbon.

5. The method in accordance with claim 4 wherein the halogenated hydrocarbon is l,l,l-trichloroethane.

6. The method in accordance with claim 1 wherein the macroorbital motion is imparted to the admixture by vibration.

7. The method in accordance with claim 1 wherein the macroorbital motion is imparted to the admixture by tumbling.

8. A method of finishing workpieces in a finishing machine which comprises admixing abrasive grains and water so as to form a slurry of mud-like consistency;

casting the slurry into a mold provided with cavities of a predetermined shape;

solidifying the slurry in said cavities into a plurality of solid chips by immersion into a bath of a liquid refrigerant comprising a material selected from the group consisting of hydrocarbons and halogenated hydrocarbons chilled to a temperature below the solidification temperature of the slurry; recovering the solid chips from said bath; admixing the recovered chips with workpieces to be 6 finished; imparting macroorbital motion to the resulting admixture; and circulating the chilled liquid refrigerant from the bath through the vibrating admixture. 9. The method in accordance with claim 8 wherein the liquid refrigerant is mineral spirits.

10. The method in accordance with claim 8 wherein the liquid refrigerant is naphtha.

11. The method in accordance with claim 8 wherein the liquid refrigerant is a halogenated hydrocarbon.

12. The method in accordance with claim 1 1 wherein the halogenated hydrocarbon is l,l,l-trichloroethane. 13. The method in accordance with claim 8 wherein the macroorbital motion is imparted to the admixture by vibration.

14. The method in accordance with claim 8 wherein the macroorbital motion is imparted to the admixture by tumbling. 

2. The method in accordance with claim 1 wherein the liquid refrigerant is mineral spirits.
 3. The method in accordance with claim 1 wherein the liquid refrigerant is naphtha.
 4. The method in accordance with claim 1 wherein the liquid refrigerant is a halogentated hydrocarbon.
 5. The method in accordance with claim 4 wherein the halogenated hydrocarbon is 1,1,1-trichloroethane.
 6. The method in accordance with claim 1 wherein the macroorbital motion is imparted to the admixture by vibration.
 7. The method in accordance with claim 1 wherein the macroorbital motion is imparted to the admixture by tumbling.
 8. A method of finishing workpieces in a finishing machine which comprises admixing abrasive grains and water so as to form a slurry of mud-like consistency; casting the slurry into a mold provided with cavities of a predetermined shape; solidifying the slurry in said cavities into a plurality of solid chips by immersion into a bath of a liquid refrigerant comprising a material selected from the group consisting of hydrocarbons and halogenated hydrocarbons chilled to a temperature below the solidification temperature of the slurry; recovering the solid chips from said bath; admixing the recovered chips with workpieces to be finished; imparting macroorbital motion to the resulting admixture; and circulating the chilled liquid refrigerant from the bath through the vibrating admixture.
 9. The method in accordance with claim 8 wherein the liquid refrigerant is mineral spirits.
 10. The method in accordance with claim 8 wherein the liquid refrigerant is naphtha.
 11. The method in accordance with claim 8 wherein the liquid refrigerant is a halogenated hydrocarbon.
 12. The method in accordance with claim 11 wherein the halogenated hydrocarbon is 1,1,1-trichloroethane.
 13. The method in accordance with claim 8 wherein the macroorbital motion is imparted to the admixture by vibration.
 14. The method in accordance with claim 8 wherein the macroorbital motion is imparted to the admixture by tumbling. 